Reportedly, 55-year-old Kim has a history of unpredictable behavior and nationalistic activism. He was arrested in 2010 for throwing pieces of concrete at the Japanese ambassador to South Korea.
Witnesses said Kim called for the reunification of South and North Korea during the Thursday attack on Lippert, which was carried out as the ambassador was just about to deliver a speech at a breakfast meeting at Sejong Hall in Seoul. Kim also called for an end to joint annual military exercises carried out by South Korea and the United States.
According to CNN, police say Kim could be charged with attempted murder.
Meanwhile, according to US State Department deputy spokesperson Marie Harf, Mark Lippert is recovering at the hospital after undergoing surgery to treat wounds to his face and hand that Kim inflicted on him using a knife.
CNN reported citing Dr. Jung Nam-shik from the Yonsei Severance Hospital that Lippert got 80 stitches to his face and will probably remain hospitalized for three or four days.
Harf said on Thursday that US law enforcement was coordinating closely with the Korean National Police but could not "speculate on a motive" behind the Lippert attack at that time.
The US Ambassador wrote on his Twitter page that he would be back "ASAP" to "advance" the alliance between the United States and South Korea.
Meanwhile the official North Korean news agency has said that the country's government believes the attack on Lippert is a just punishment for the United States.
Long-term tensions on the Korean Peninsula escalated last month, when Pyongyang accused Seoul and Washington of rejecting an invitation to visit the country and pointing out the Southern allies' unwillingness to resume denuclearization talks.
North Korea proposed that Washington suspend the joint military drills conducted every year with South Korea in January, saying that in response it would temporarily halt its nuclear testing.
North and South Korea are technically in a state of war, as no formal peace treaty has been signed following the 1950-1953 Korean War.